Experimental and clinical observations have supported the concept that the hypothalamus plays a key role in the regulation of adenohypophysial corticotropic cells' secretory functions. Over 40 years ago it was demonstrated that factors present in the hypothalamus would increase the rate of ACTH secretion by the pituitary gland when incubated in vitro or maintained in an organ culture. However, a physiologic corticotropin releasing factor (CRF) was not characterized until ovine CRF (OCRF) was characterized in 1981. As disclosed in U.S. Pat. No. 4,415,558, the disclosure of which is incorporated herein by reference, oCRF was found to be a 41-residue amidated peptide. oCRF lowers blood pressure in mammals when injected peripherally and stimulates the secretion of ACTH and .beta.-endorphin.
Rat CRF (rCRF) was later isolated, purified and characterized; it was found to be a homologous, amidated hentetracontapeptide as described in U.S. Pat. No. 4,489,163, the disclosure of which is incorporated herein by reference. The amino acid sequence of human CRF has now been determined to be the same as that of rCRF. rCRF and hCRF are used interchangeably, and the designation r/hCRF is frequently used with respect to this peptide hormone. These peptide hormones may be considered to form a part of a larger family of native CRF-like peptides and analogs which include the mammalian and fish CRFs, the urotensins and sauvagine, as discussed in Vale et al., "Characterization of the Hypothalamic Peptide: Corticotropin Releasing Factor", Proceedings of the Naito International Symposium on Natural and Biological Activity, Tokyo, Japan, Nov. 5-7, 1985, and Lederis et al., "Neurohormones from Fish Tails, II: Actions of Urotensin I in Mammals and Fishes", Recent Progress in Honnone Research, Vol. 41, Academic Press, Inc. (1985).
Although originally isolated and characterized on the basis of its role in this hypothalamopituitary-adrenal (HPA) axis, CRF has been found to be distributed broadly throughout the central nervous system as well as in extraneural tissues, such as the adrenal glands, placenta and testes, where it may also act as a paracrine regulator or a neurotransmitter. Moreover, the likely involvement of CRF in affective disorders, such as anxiety, depression, alcoholism and anorexia nervosa, and in modulating reproduction and immune responses suggests that changes in CRF expression may have important physiological and pathophysiological consequences. For example, perturbations in the regulatory loops comprising the HPA axis often produce chronically elevated levels of circulating glucocorticoids; such patients display the physical hallmarks of Cushing's syndrome, including truncal obesity, muscle-wasting, and reduced fertility.
In addition to its role in mediating activation of the hypothalamic-pituitary-adrenal, CRF has also been shown to modulate autonomic and behavioral changes, some of which occur during the stress response. Many of these behavioral changes have been shown to occur independently of HPA activation in that they are not duplicated by dexamethasone treatment and are insensitive to hypophysectomy. In addition, direct infusion of CRF into the CNS mimics autonomic and behavioral responses to a variety of stressors. Because peripheral administration of CRF or a CRF antagonist fails to affect certain of these changes, it appears that CRF exhibits a direct brain action with respect to such functions, which include appetite suppression, increased arousal and learning ability. However, CRF antagonists given peripherally attenuate stress-mediated increases in ACTH secretion, and when delivered into the cerebral ventricles can mitigate stress-induced changes in autonomic activity and behavior.
As a result of the extensive anatomical distribution and multiple biological actions of CRF, this regulatory peptide is believed to be involved in the regulation of numerous biological processes. CRF has also been implicated in the regulation of inflammatory responses. Although it has been observed that CRF plays a pro-inflammatory role in certain animal models, CRF appears to suppress inflammation in others by reducing injury-induced increases in vascular permeability.
A CRF analog having a high alpha-helical forming potential was developed in about early 1984. It is a 41-residue amidated peptide commonly referred to as AHC (alpha-helical CRF) and is described in U.S. Pat. No. 4,594,329, the disclosure of which is incorporated herein by reference; it is considered to now be a member of the overall family of CRF-like peptides. Other CRF analogs containing D-isomers of .alpha.-amino acids were developed, such as those shown in U.S. Pat. No. 5,278,146. Synthetic r/hCRF, OCRF and AHC all stimulate ACTH and .beta.-endorphin-like activities (.beta.-END-Li) in vitro and in vivo and substantially lower blood pressure when injected peripherally. Antagonists of these three peptides and of sauvagine and urotensin are disclosed in U.S. Pat. No. 4,605,642, issued Aug. 12, 1986, the disclosure of which is incorporated herein by reference. Cyclic CRF antagonists exhibiting biopotency were earlier developed as disclosed in U.S. Pat. No. 5,245,009 (Sep. 14, 1993) and in pending U.S. patent application Ser. No. 78,558, filed Jun. 16, 1993, for which the issue fee was paid.
Since the foregoing discoveries, the search for improved CRF antagonists has continued.